I don't think the foreshortening on the left (his right) leg is working. It also looks kinda noodly :/

I'm no anatomy expert, but at a glance, his abdomen looks a little short.

Even though there's no "head" on this figure per se, did you draw a head anyway before constructing the rest of the body? Even without a head, all proportions should still be relative to some kind of head size.

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"Trying is the first step towards failure." -Homer Simpson"Sucking at something is the first step towards being sorta good at something." -Jake the Dog

I think that if you're going to be studying anatomy from Loomis's work then drawing a realistic pokemon is not the right approach. The anatomy is off in places and the eyes are rendered as if they were in a skull and not on a fantastical creature that has only eyes in it's chest. It really triggers a weird "uncanny valley" feel and I immediately see everything wrong with it.
I can see that you rendered part of a nose bridge on the chest between the two eyes. Nose bridges only exist on things that have...a nose...What I'm trying to get at is that you shouldn't be using a pokemon to study anatomy, they're not real creatures, they weren't thought out as deeply as you're trying to get at, so they can only be rendered nicely in a hyper realistic way by people who know what they're dealing with. Honestly I would leave this piece and start something else. Maybe you can come back to it when you have a better understanding of shape, anatomy and form. (I'm not trying to put you down btw, I just don't want you to learn any bad habits by accident.)

That being said, You should not shade with black, always flattens things out. Use a bigger brush size and it will help the whole painting look more put together, right now it's really scratchy and just overall messy looking. A larger brush with a higher opacity will give you a more "buttery" feel to your painting. Honestly messing with Opacity is a bad choice as well(I had to unlearn it so I know it's allure). Try just setting the flow to your pen pressure rather than opacity.